Device for sample injection in gas chromatographs

ABSTRACT

In prior sample introduction systems for a gas chromatograph of the type where sealed sample vessels are inserted by a cartridgelike plunger and the vessel is then opened within the inlet to the chromatograph to release the sample, the carrier gas flow &#39;&#39;&#39;&#39;collapses&#39;&#39;&#39;&#39; whenever the cartridge-like plunger is withdrawn since the system is opened to atmosphere. The carrier gas flow controller requires a long time to build up normal flow again, and also air is allowed to enter the carrier gas system. To eliminate these problems a gate is included in the inlet section which closes off the path to atmosphere before the carrier gas system is connected to this gate. As the cartridge plunger closes off the atmospheric end of this gate, a &#39;&#39;&#39;&#39;dummy&#39;&#39;&#39;&#39; piston moves along with the cartridge to open a volume equal to the volume displaced by the advancing cartridge, so that no pump action occurs. Preferably the gate is filled with carrier gas as the plunger is inserted to avoid introduction of air into the system.

' United States Patent [191 one et al.

[54] DEVICE FOR SAMPLE INJECTION IN GAS CHROMATOGRAPIIS [75 inventors: ginlrard Otte, 777 Uberlingen;

Gisela warmer; 775 matinee Wollmatingen; Willi Schwelkel, 7777 Unteruhldingen, all of Germany [73] Assignee: Bodenseewerk Perkin-Elmer 81 Co.

GIIIbII, Ueberlingen/Bodensee, Germany [22] Filed: Oct. 28, 1971 [21] Appl.No.: 193,395

[30] Foreign Application Priority Data Harris ..13/422 oc 1 Jan. 16, 1973 3,672,227 6/1972 Frank ..73/422 GC Primary Examiner-S. Clement Swish Attorney-Edward R. Hyde, Jr.

[57] ABSTRACT In prior sample introduction systems for a gas chromatograph of the type where sealed sample vessels are inserted by a cartridge-like plunger and the vessel is then opened within the inlet to the chromatograph to release the sample, the carrier gas flow collapses whenever the cartridge-like plunger is withdrawn since the system is opened to atmosphere. The carrier gas flow controller requires a long time to build up normal flow again, and also air is allowed to enter the carrier gas system. To eliminate these problems a gate is included in the inlet section which closes off the path to atmosphere before the carrier gas system is connected to this gate. As the cartridge plunger closes off the atmospheric end of this gate, a dummy piston moves along with the cartridge to open a volume equal to the volume displaced by the advancing cartridge, so that no pump action occurs. Preferably the gate is filled with carrier gas as the plunger is inserted to avoid introduction of air into the system.

8 Claims, 7 Drawing Figures PATENTEDJAH 16 1975 SHEET 0F 7 PATENTEDJAHIS I975 3.710 628 sum 5 OF 7 Fig. 5

DEVICE FOR SAMPLE INJECTION IN GAS CHROMATOGRAPIIS BACKGROUND OF THE INVENTION This invention relates to a device for introducing the sample in gas chromatographs especially of the type in which the samples are contained in a series of scaled vessels, each of which is held and inserted by a cartridge-like plunger into the inlet section of the gas chromatograph, and the sample vessels are ruptured thereby releasing the samples, for instance, by being pierced by means of a punch.

It is prior art to inject liquid or solid samples into analytical apparatus including a carrier gas circulating system in such a manner that the sample is originally sealed in a metallic vessel by mechanical deformation of the latter. The metallic vessel is pierced by a punch in the inlet section and its contents is carried by a carrier gas stream into the carrier gas flow system, for instance to a separating" column. For this purpose, the vessels are inserted in a cartridge (i.e., an open-ended plunger) which is moved into a guide sleeve aligned with the punch. The cartridge is substantially formed of a rod carrying resilient fingers or a collet (forming a cavity) At its end releasably supporting the vessel. The carrier gas stream through the system (including the separating column), is maintained constant by a flow controller. After completion of the analysis, the cartridge with the pierced vessel is withdrawn, the pierced vessel removed from the cartridge, and another sample vessel inserted and treatedin the same manner. A device for automation of this sample injecting action has also been proposed already.

In prior devices of the type indicated immediately above, the following problem is encountered. When changing vessels by withdrawing (and replacing) the cartridge, the carrier gas circulating system is opened at the inlet side to the atmosphere. The carrier gas flow through the separating column immediately collapses. The flow controller needs a relatively long period of time after the'system is againsealed before constant controlled'gas flow is again obtained. This involves two disadvantages:

a. In the case of separating columns of high charge (e.g., heavy coating of separating liquid) which are run at a high temperature, a flame ionization detector normally indicates a continuous signal caused by bleeding" of the separating column. This signal is represented by a parallel shift of the zero line by about two orders ofmagnitude tol0" amps). With a variation of the carrier gas flow, the rate of the transfer to the detector'of the separating substance from the bleeding of the separating column also changes, and' the detector zero line tends to be disturbed. When using a carrier gas flow controller, this disturbance may have not completely disappeared when the first possible gas chromatographicpeak occurs.

b. Since the individual retention times of any particular gas chromatographic peakand of the air peak (time of "break-through") are differently and greatly affected (made too long) due to the exponential rise of the carrier gas flow rate (from zero), the relative retention times will be "falsified (i.e., disproportionally changed) in comparison to the values measured using conventional sample injection by-means of a syringe.

Normally there is a linear relationship between the logarithm of the relative retention time and the number of carbon atoms in groups of homologs; but in a system opened repeatedly in the described manner, this relationship is also adversely affected (i.e., the linearity destroyed). Another disadvantage of the prior devices is that with each sample injection an undesired amount of air enters into the system.

It is therefore an object of this invention to avoid the described'disadvantages of the prior devices.

It is a more specific object of this invention to provide a device of the type mentioned hereinbefore (using separate sample vessels), in which even during sample (vessel) introduction a substantially constant carrier gas flow through the entire system is ensured.

Another object of the invention is to avoid the admission of air into the carrier gas system during sample introduction.

The broadest concepts of the invention include the fact that the introduction of the cartridge into the inlet section is effected through a gate by which communication to the atmosphere can be shut off before the sample is released into the carrier gas carrying system of the gas chromatograph, and that the sample (vessel) carrying cartridge is coupled with a dummy piston sliding in a pressure-balancing cylinder connected with the carrier gas carrying system so as to provide a com pensating volume equal to the volume displaced by insertion of the cartridge (and the sample vessel).

By the use of a gate which shuts 05 communication to the atmosphere before the cartridge enters into the 7 carrier gas carrying system, a collapse of the pressure (i.e., reduction to atmospheric pressure) and therefore the flow of the carrier gas is prevented when the cartridge is changed. However, when the cartridge is moved into such a sealed system, an undesired pressure rise would be caused at the inlet of the separating column as well as an increase in flow through the separating column, since the cartridge moving into the sealed system would act like a pump piston. In order to avoid this pressure rise, which of course is also disadvantageous, another aspect of the invention includes the provision of a dummy piston which is moved together with the cartridge and releases a compensating volume which is equal to the volume displaced by the cartridge being introduced.

A further feature of the invention includes (in an arrangement according to the above) avoiding the penetration of air into the system by introducing a stream of carrier gas into the gate so that it is constantly rinsed with carrier gas, thereby keeping air from being entrapped when the sealing occurs.

An illustrative embodiment of this invention will now be described in greater detail with reference to the accompanying drawings, in which:

FIG. I is a schematic representation of a device incorporating the invention;

FIG. 2 is a structural representation of the inlet section of the device with the gate closed both to atmosphere and on the system side;

FIG. 3 is a similar representation of the inlet section but with the gate open on the system side;

FIG. 4 is a detailed representation of the dummy piston; and

FIGS. 5 to 7 are comparative graphical illustrations of the advantages obtained with the device incorporating the invention relative to prior devices.

In an exemplary gas chromatograph according to the invention in FIG. 1, the inlet section generally referenced 10 comprises a guide sleeve 12 which is followed by an enlarged chamber 14. An extension 16 accommodating a punch 18 is provided on the opposite side of the chamber 14 in alignment with the guide sleeve 12. The punch 18 has a longitudinal central channel 20 which is in communication with (the entrance end of) a gas chromatographic separating column 22. Reference numeral 24 generally designates a cartridge for the introduction of samples, the samples being in a liquid or solid state and contained in sealed metallic vessels 26. The cartridge 24 comprises a rod 28 having at its end means (e.g., a spring collet) forming a resilient cavity 30 for the vessel 26. The end portion 32 of the rod 28 is narrower than the remaining portion. The thicker portion of the rod 28 is sealingly slidable in the guide sleeve 12 as by means of an O-ring 34. This seal effects the shutoff to atmosphere of the gate or inlet 36 provided by the guide sleeve 12. Towards the carrier gas carrying flow system of the gas chromatograph, the opposite end of the inlet or gate 36 (i.e., the interior of the guide sleeve 12) is shut off by a spring-loaded flap 38 which can be forcibly rotated inwardly against the action of the spring.

Reference numeral 40 designates a (pressurized) carrier gas source which is in communication with the enlarged chamber 14 through a pressure controller 42 and a flow controller 44. Between the pressure controller 42 and the flow controller 44 a branch conduit is connected. A butterfly valve 48 acting as a variable pressure dropping throttle, a storage volume 50 and a valve 52 are arranged in this branch 46, the other end of which is connected into the interior of the gate 36, directly in front of the flap 38. The valve 52 is preferably actuated automatically by the cartridge 24 in a manner not shown, so as to open valve 52 when the cartridge is inserted approximately to the position shown in FIG. 1, that is, shortly before the gate 36 is closed by the O-ring 34.

FIGS. 2 and 3 illustrate a structural embodiment of the inlet section including the gate. The guide sleeve 12 defining the gate 36, terminates in a flange 54. On the flange 54 is mounted a cup shaped housing 56 forming the chamber 14 and provided with a sleeve or a collar 58 in alignment with the sleeve 12. A closing element 60 including a punch 18 is inserted into sleeve 58; the separating column is connected to the carrier gas channel 20 formed in punch 18 and insert 60. The flap or hinged door 38 is pivoted to the flange 54 as at 39 and is biased in the closed direction by an expanding spring 41. In the flange 54 a central dovetail recess 62 accom- 'modates a gasket 64. This gasket 64 ensures a tight seal of the gate in its end towards the carrier gas carrying system, when the flap 38 rests thereon (i.e., is closed) as shown in FIG. 2.

Carrier gas is introduced from the flow controller 44 (FIG. 1) into the chamber 14 through a channel 66 as is indicated by the arrow B. Communication through a channel 68 is established to a pressure-balancing cylinder 70 in a manner to be described hereinafter. Through channel 72, which terminates in the dovetail recess 62 underneath the flap, a rinsing portion of the carrier gas is introduced from the storage volume 50 through the branch conduit 46 into gate 36 when the valve 52 is opened.

The pressure-balancing cylinder (as schematically shown in FIG. 1) extends parallelly to the guide sleeve 12. A dummy piston 74, including a piston rod 76 guided in a bearing 78, slides in the cylinder 70. The piston rod 76 has a collar 80. On the cartridge 24 (or a cartridge holder connected thereto) a driver 82 is mounted which, when the cartridge is introduced (upwardly in FIG. 1), is caused to abut the collar specifically at that point in its movement when the seal 34 shuts off the gate 36 to the atmosphere. The driver 82 then carries along the dummy piston 74 (by means of the piston rod 76) against the action of a return spring 84. Thus the piston 74 during its movement upwardly in FIG. 1 releases" (i.e., opens) a volume in the cylinder 70, which will equal that displaced by the inwardly moving cartridge 24, if both have the same cross sectional area (and move the same linear amount in their longitudinal direction). By means of the channel 68 and the connection C chamber 14 is connected to the interior chamber 71 of the cylinder 70 so that the total volume of chamber 71 and the interior 36 of the inlet gate remains constant, and no pressure rise is caused by insertion of the cartridge 24. In a position of rest (in the piston inserted direction, corresponding to the cartridge being removed) the collar 80 abuts an adjustable stop 86, limiting the movement of piston 74 in the cylinder 70 under the influence of spring 84. By adjustment of stop 86, it can be ensured that the stoke of the piston 74 begins just as the sealing of the gate to the atmosphere is effected by the seal 34.

FIG. 4 illustrates a structural embodied form of the pressure-balancing arrangement. The outermost position of the dummy piston, corresponding to when the cartridge is fully inserted, is shown in solid lines, while the dotted lines illustrate the position of rest (vi/hen the cartridge is removed). A driving plate 82 on the cartridge holder is used as the driver element. The stop.86 is adjustably mounted to a frame 92 as by oblong holes 88 and clamping screws 90. Assuming elements 12 and 70 are both cylindrical interiorly, they merely need be of the same diameter to cause exact volume compensation as the plunger 24 and piston 74 are moved.

The arrangement hereinbefore described operates as follows. The vessel 26, containing the sample therein, is inserted into the cavity 30 at the end 32 of the cartridge 24 (which of course is completely withdrawn from the sleeve 12). It is retained therein in known manner by resilient fingers. The carrier gas carrying system of the gas chromatograph is at this time shut off from the atmosphere by the flap 38 under the influence of the spring 41. Carrier gas from a carrier gas source 40 has its pressure controlled by the pressure controller 42 and the flow controller 44 supplies a desired, accurately defined gas flow to the system (i.e., to chamber 14 and column 22, etc.). In front of the flow controller 44 carrier gas flows into the branch conduit 46. The carrier gas stream flowing through this branch conduit is adjusted by valve 48, acting as an adjustable throttle, so that the control by the flow controller 44 is not impaired by this branched-off carrier gas stream. The storage volume 50 is filled up through the throttle.

Then the cartridge 24 with the vessel 26 is introduced, in the manner illustrated in FIG. 1, into the guide sleeve 12, the interior of which alsoconstitutes-the gate 36. Shortly before the seal 34 reaches the guide sleeve 12 and thereby shuts off the (lower end of the) gate 36 to the atmosphere, the valve 52 is opened automatically. Thereby, a carrier gas stream is supplied from the storage volume 50 to the gate 36 (through-channel 72 in FIG. 2) by which the air in the gate 36 is rinsed out. Then the seal 34 shuts off the gate 36 towards the atmosphere (see FIG. 2). Soon thereafter the flap 38 is forced open by the vessel 26, at the upper end of the cartridge, whereby communication is established between the gate and the rest of the system, through which the carrier gas is circulating. Thus, when introducing the cartridge with the vessel 26, the system (i.e., the main carrier gas supply and the column, etc.) is never open to atmosphere. The flow through the separating column 22 therefore always remains unchanged. As the cartridge 24 is advanced beyond the point of sealing by seal 34 (i.e., approximately the position shown in FIG. 2), the driver 82 carries along the dummy piston 74 by means of the collar 80 and the piston rod 76. Since the sum of the gas volumes in the chamber 14 and in the cylinder chamber 71 remains constant, no pressure increase (which would otherwise be caused by the pump action of the cartridge sliding into gate 36) occurs by the introduction of the cartridge. Finally, the vessel 26 is opened by being pierced through by the punch 18, and the sample substance contained in the vessel is swept into the separating column by the carrier gas stream. The inlet section can be heated in the conventional manner, which is not illustrated herein.

FIGS. 5 to 7 illustrate the advantages obtained by the arrangement according to the invention over against the prior devices.

FIG. 5. shows at A a graph representing the logerithm of the relative retention times with respect to the carbon number of homologues (indicated at C5-C8). A deviation of the measured values (at the points shown) with respect to the straight line theoretically predicted can be noticed. These measurements were carried out with an open system, that is, in which the system is opened (to atmosphere) each time a cartridge with the next sample vessel is introduced.

At B in FIG. 5 the respective measurements (again, of the logarithm of retention times in the separating column versus the number of carbons in each of the homologically related compounds in the sample) with a system constructed in accordance with the invention are illustrated, and the strictly linear relation is readily noticeable.

FIG. 6 shows at the left side A the zero line disturbances of a hot wire detector output signal caused by the prior system being opened during sample injection, even when using non-bleeding separating columns. The left-hand half of diagram A shows at 100 the disturbance caused by introduction of the cartridge plunger in an actual chromatogram, in which the sample components designated C5-C8 were the straight chain saturated hydrocarbons'of the indicated carbon numbers (i.e., pentane, hexane, heptane and octane, respectively). As indicated, the right-handhalf of diagram A (and diagram B, yet to be described) was obtained when an empty sample vessel was introduced (i.e., no actual sample). Since (as is usual in chromatograms) the time scale of all parts of FIG. 6 reads from right to left, the disturbance 104 in the right-hand half (i.e., blank sample) of diagram A occurred after (and was caused by) introduction of the cartridge plunger; while the base line disturbance at 102 was caused by withdrawal of the plunger.

The diagram 8" in FIG. 6 shows similar comparison (i.e., both actual sample and blank sample) measurements with a device in accordance with the invention. It can be seen that the aforesaid disturbances no longer occur. The measurements of FIG. 6 were all carried out with hot wire detectors, and the measurements A and B were made under the same conditions and with the same sensitivity (i.e., detector amplification gain).

FIG. 7 shows in measured graphical form, also obtained underidentical conditions, zero line disturbances as they occur when using a flame ionization detector with a column having a bleeding separating substance. Here too, it can be seen that in the prior art system (at A) strong, relatively slowly fading zero line deviations occur due to the system being opened during sample injection. In particular, as the system is opened the drop in carrier gas pressure and therefore substantial stopping of its flow through the column causes the detector substantially to stop receiving the bleeding separating substance; the detector output signal therefore rapidly falls (e.g., from 10' to 10 amps). When the system is again closed, the carrier gas (pressure and therefore) flow starts to rise causing the bleeding substance to be fed to the detector at an increasing rate. Finally there is a temporary overshoot" (which may occur during arrival of early sample components, such as methane, as indicated). Presumably this bleeding peak is caused because the part of the carrier gas which was in the column for a relatively long time (while the flow was substantially stopped) is richer in bled separating substance than obtained during the dynamic equilibrium between bleeding substance and the normal flow rate of gas. These deviations are substantially eliminated or at least very greatly reduced with a system according to the invention (as may be seen at B).

We claim:

1. In a device for sample introduction into gas chromatographs having a carrier gas circulating system wherein the samples are contained in sealed vessels releasably held by a plunger which is inserted into the inlet section of the chromatograph and the sample vessel then opened to release the sample, the improvement comprising:

a closable gate (36) through which the plunger (24) is inserted;

said gate being of such. construction that insertion of said plunger closes its one end communicating with the atmosphere before its other end is opened into communication with the carrier gas circulating system of the gas chromatograph;

a dummy piston (74) slidable in a pressure-balancing cylinder operatively connected to said plunger, of such construction as to open a compensating volume equal to the volume displaced by said plunger upon its insertion through said gate after its said one end is closed,

whereby the carrier gas flow is maintained substantially constant during removal and insertion of said plunger, and the potentially pressure-disturbing pump action of the plunger upon insertion is compensated by movement of said dummy piston in said pressure-balancing cylinder.

2. The device claimed in claim 1, in which:

said plunger comprises a rod (28) the end of which releasably carries said vessel in a cavity defined by resilient means;

said gate comprises a guide sleeve (12) slidably receiving said plunger;

said plunger comprises an end portion of reduced diameter followed by an enlarged portion having a cross section substantially equal to the interior cross section of said sleeve;

sealing means are provided for sealing said enlarged cross section portion of said plunger within said sleeve upon partial insertion of said plunger;

a hinged door (38) spring loaded toward a closed position, is positioned at the other remote end of said sleeve communicating with said carrier gas circulating system, said door being in the path of and therefore opened by the end of said plunger rod upon its further insertion into said sleeve,

whereby, upon insertion of said plunger, the atmosphere end of said sleeve is first sealed and then the other end of said sleeve is subsequently opened to communicate with the gas carrying part of the chromatograph.

3. The device as claimed in claim 2, in which:

an enlarged chamber (14) is connected to said other remote end of said sleeve, said chamber receiving the main carrier gas flow of said chromatograph and also being connected to said pressure balancing cylinder;

a sample vessel opening means is positioned within said chamber on the side opposite from and in alignment with said other remote end of said sleeve, said vessel opening means including a channel means in connecting relationship to the separating column of said chromatograph,

whereby further insertion of said plunger causes opening of said sample vessel and therefore introduction of the sample therein into the separating column of the chromatograph without disturbing the pressure and flow of the carrier gas within the chromatograph.

4. A device as claimed in claim 2 in which:

said dummy piston is movable out of said pressure balancing cylinder along a direction parallel to the direction of insertion of said plunger;

said dummy piston is rigidly attached to a piston rod (76) carrying a collar means;

return spring means (84) resiliently urges said piston rod and therefore said piston into said pressure balancing cylinder;

driving means (82) is operatively connected to said plunger for engaging said piston rod collar and moving said piston against said spring out of said cylinder when said plunger has moved to its sealing position within said sleeve;

whereby said dummy piston starts to move as said plunger moves within the now sealed sleeve, thereby compensating the pump action which would otherwise occur upon further insertion of said plunger.

5. The device as claimed in claim 4, in which:

an adjustable stop means (86) operatively engages said collar means for limiting movement of said piston rod and therefore said piston in the direction urged by said return spring means,

whereby said adjustable stop means determines the maximum extent that the piston enters the pressure balancing cylinder and therefore determines the position of the plunger at which its driving means engages the piston rod collar for initiating movement of the piston out of the cylinder.

6. The device as claimed in claim 1, in which:

an auxiliary carrier gas supply means is connected to the interior of said gate;

and a control means is provided for causing carrier gas to flow through said auxiliary supply means at least shortly before said plunger closes said one end of said gate,

whereby said gate is supplied with carrier gas,

thereby rinsing out any air contained therein before its one end is closed, thereby avoiding the trapping of air within the gate and inlet section of the chromatograph.

7. The device as claimed in claim 6, in which:

said carrier gas circulating system of the chromatograph comprises in series a carrier gas source, a pressure controller and a flow controller;

said auxiliary carrier gas supply means comprises a branch conduit (46) connected to said circulating system between said pressure controller and said flow controller;

said branch conduit comprising in series a pressuredropping throttle means (48), a storage volume (50), a valve (52), and a channel means (72) connecting to the interior of said gate;

said valve being adapted to open so as to cause a supply of carrier gas to the interior of said gate before its one end is closed by said plunger,

whereby the carrier gas within said storage volume is supplied through said channel to the interior of said gate to rinse out the air contained therein before the one end of the gate is closed, without causing any disturbance in the pressure and therefore the flow of the carrier gas circulating system supplying the chromatograph.

8. The device as claimed in claim 7, in which:

said plunger comprises a rod (28) the end of which releasably carries said vessel in a cavity defined by resilient means;

said gate comprises a guide sleeve (12) slidably receiving said plunger;

said plunger comprises an end portion of reduced diameter followed by an enlarged portion having a cross section substantially equal to the interior cross section of said sleeve;

sealing means are provided for sealing said enlarged cross section portion of said plunger within said sleeve upon partial insertion of said plunger;

a hinged door (38), spring loaded toward a closed position, is positioned at the other remote end of said sleeve communicating with said carrier gas circulating system, said door being in the path of and therefore opened by the end of said plunger rod upon its further insertion into said sleeve; 

1. In a device for sample introduction into gas chromatographs having a carrier gas circulating system wherein the samples are contained in sealed vessels releasably held by a plunger which is inserted into the inlet section of the chromatograph and the sample vessel then opened to release the sample, the improvement comprising: a closable gate (36) through which the plunger (24) is inserted; said gate being of such construction that insertion of said plunger closes its one end communicating with the atmosphere before its other end is opened into communication with the carrier gas circulating system of the gas chromatograph; a dummy piston (74) slidable in a pressure-balancing cylinder (70), operatively connected to said plunger, of such construction as to open a compensating volume equal to the volume displaced by said plunger upon its insertion through said gate after its said one end is closed, whereby the carrier gas flow is maintained substantially constant during removal and insertion of said plunger, and the potentially pressure-disturbing pump action of the plunger upon insertion is compensated by movement of said dummy piston in said pressure-balancing cylinder.
 2. The device claimed in claim 1, in which: said plunger comprises a rod (28) the end of which releasably carries said vessel in a cavity defined by resilient means; said gate comprises a guide sleeve (12) slidably receiving said plunger; said plunger comprises an end portion of reduced diameter followed by an enlarged portion having a cross section substantially equal to the interior cross section of said sleeve; sealing means are provided for sealing said enlarged cross section portion of said plunger within said sleeve upon partial insertion of said plunger; a hinged door (38) spring loaded toward a closed position, is positioned at the other remote end of said sleeve communicating with said carrier gas circulating system, said door being in the path of and therefore opened by the end of said plunger rod upon its further insertion into said sleeve, whereby, upon insertion of said plunger, the atmosphere end of said sleeve is first sealed and then the other end of said sleeve is subsequently opened to communicate with the gas carrying part of the chromatograph.
 3. The device as claimed in claim 2, in which: an enlarged chamber (14) is connected to said other remote end of said sleeve, said chamber receiving the main carrier gas flow of said chromatograph and also being connected to said pressure balancing cylinder; a sample vessel opening means is positioned within said chamber on the side opposite from and in alignment with said other remote end of said sleeve, said vessel opening means including a channel means in connecting relationship to the separating column of said chromatograph, whereby further insertion of said plunger causes opening of said sample vessel and therefore introduction of the sample therein into the separating column of the chromatograph without disturbing tHe pressure and flow of the carrier gas within the chromatograph.
 4. A device as claimed in claim 2 in which: said dummy piston is movable out of said pressure balancing cylinder along a direction parallel to the direction of insertion of said plunger; said dummy piston is rigidly attached to a piston rod (76) carrying a collar means; return spring means (84) resiliently urges said piston rod and therefore said piston into said pressure balancing cylinder; driving means (82) is operatively connected to said plunger for engaging said piston rod collar and moving said piston against said spring out of said cylinder when said plunger has moved to its sealing position within said sleeve; whereby said dummy piston starts to move as said plunger moves within the now sealed sleeve, thereby compensating the pump action which would otherwise occur upon further insertion of said plunger.
 5. The device as claimed in claim 4, in which: an adjustable stop means (86) operatively engages said collar means for limiting movement of said piston rod and therefore said piston in the direction urged by said return spring means, whereby said adjustable stop means determines the maximum extent that the piston enters the pressure balancing cylinder and therefore determines the position of the plunger at which its driving means engages the piston rod collar for initiating movement of the piston out of the cylinder.
 6. The device as claimed in claim 1, in which: an auxiliary carrier gas supply means is connected to the interior of said gate; and a control means is provided for causing carrier gas to flow through said auxiliary supply means at least shortly before said plunger closes said one end of said gate, whereby said gate is supplied with carrier gas, thereby rinsing out any air contained therein before its one end is closed, thereby avoiding the trapping of air within the gate and inlet section of the chromatograph.
 7. The device as claimed in claim 6, in which: said carrier gas circulating system of the chromatograph comprises in series a carrier gas source, a pressure controller and a flow controller; said auxiliary carrier gas supply means comprises a branch conduit (46) connected to said circulating system between said pressure controller and said flow controller; said branch conduit comprising in series a pressure-dropping throttle means (48), a storage volume (50), a valve (52), and a channel means (72) connecting to the interior of said gate; said valve being adapted to open so as to cause a supply of carrier gas to the interior of said gate before its one end is closed by said plunger, whereby the carrier gas within said storage volume is supplied through said channel to the interior of said gate to rinse out the air contained therein before the one end of the gate is closed, without causing any disturbance in the pressure and therefore the flow of the carrier gas circulating system supplying the chromatograph.
 8. The device as claimed in claim 7, in which: said plunger comprises a rod (28) the end of which releasably carries said vessel in a cavity defined by resilient means; said gate comprises a guide sleeve (12) slidably receiving said plunger; said plunger comprises an end portion of reduced diameter followed by an enlarged portion having a cross section substantially equal to the interior cross section of said sleeve; sealing means are provided for sealing said enlarged cross section portion of said plunger within said sleeve upon partial insertion of said plunger; a hinged door (38), spring loaded toward a closed position, is positioned at the other remote end of said sleeve communicating with said carrier gas circulating system, said door being in the path of and therefore opened by the end of said plunger rod upon its further insertion into said sleeve; and said channel means of said branch conduit terminates closely adjacent said hinged door in the other remoTe end of said sleeve, whereby the entire interior of said sleeve is supplied with carrier gas and therefore rinsed free of air before the one end thereof is closed by said plunger. 